The glandular kallikreins are a subgroup of serine proteases which are involved in the post-translational processing of specific polypeptide precursors to their biologically active forms. The human kallikrein gene family consists of three members: prostate-specific antigen, human glandular kallikrein, and pancreatic/renal kallikrein. See J. A. Clements, Endocr. Rev., 10, 393 (1989) and T. M. Chu et al. (U.S. Pat. No. 4,446,122). A common nomenclature for these members of the tissue (glandular) kallikrein gene families was recently adopted by T. Berg et al., in Recent Progress on Kinins: Biochemistry and Molecular Biology of the Kallikrein-Kinin System. Agents and Actions Supplements, Vol. I., H. Fritz et al.., eds., Birkkauser Verlag, Basel (1992), and is defined in Table I, below.
TABLE 1 ______________________________________ The Human Tissue Kallikrein Gene Family (approved species designation: HSA) New Previous Designa- Designa- New Protein tion tions mRNA/cDNA Protein Designation ______________________________________ hKLK1 KLK1 HK1 and tissue kalli- hK1 hRKALL phKK25 krein (renal/ cDNAs pancrease/sali- vary) hKLK2 KLK2 prostate-specific hK2 hGK-1 glandular kalli- hKK-3 krein hKLK3 PSA HPSA-1 PSA (prostate- hK3
and PSA specific antigen) APS cDNAs ______________________________________
The DNA sequence homology between hKLK2 and hKLK3 (exon regions) is 80%, whereas the homology between hKLK2 and hKLK1 is 65%. The deduced amino acid sequence homology of hK2 to hK1 is 57%. Amino acid sequences deduced by L. J. Schedlich et al., DNA 6, 429 (1987) and B. J. Morris, Clin. Exp. Pharmacol. Physiol. 16, 345 (1989) indicate that hK2 may be a trypsin-like serine protease, whereas hK3 (PSA) is a chymotrypsin-like serine protease. Therefore, if hK2 is indeed secretory, it may have a different physiological function than hK3.
The hKLK2 gene is located about 12 kbp downstream from the hKLK3 gene in a head-to-tail fashion on chromosome 19. (P. H. Riegman et al., FEBS Lett., 247, 123, (1989)). The similarities of gene structure and deduced amino acid sequences of these human kallikreins suggest that their evolution may involve the same ancestral gene. Most interestingly, as reported by Morris, cited supra; P. Chapdelaine, FEBS Lett., 236, 205 (1988); and Young, Biochemistry, 31, 1952 (1992), both hK2 and hK3 may be expressed only in the human prostate, while expression of hK1 is limited to the pancreas, submandibular gland, kidney, and other nonprostate tissues.
Tremendous interest has been generated in hK3 (PSA) because of the important role it plays as a marker to detect and to monitor progression of prostate carcinoma. Its usefulness as a marker is based on the elevated serum concentration of circulating hK3 proteins which are frequently associated with prostatic cancer. The serum concentration of hK3 has been found to be proportional to the cancer mass in untreated patients, but is also proportional to the volume of hyperplastic tissue in patients with benign prostatic hyperplasia (BPH). The serum levels of hK3 become reduced following prostate cancer therapy.
Despite the information which can be ascertained about hK2 from the genomic DNA sequence, very little is known about the hK2 polypeptide itself. The reason for this is that the protein has not been purified and characterized. Thus, a need exists for a method to obtain hK2 polypeptide and related polypeptides in sufficient quantity and purity for characterization and for use as therapeutic/diagnostic agents or reagents.